Technically, your wife received self-employment income in 2021, which is why it should be reported on a Schedule C.
Generally, for tax purposes, self-employment income includes any part-time business or "side work" performed in which she is in business for herself, rather than another person. She is also considered self-employed and needs to file a Schedule C if she engages in business-like activities where she intended to make a profit. This would include money received from doing consulting work.
Since the consulting work is for a related field, you can use the same Schedule C that was in your 2020 return.
@WitchHazel
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